Function query_cap 

unsafe fn query_cap(
    funcs: &NV_ENCODE_API_FUNCTION_LIST,
    session: *mut c_void,
    codec: GUID,
    cap: NV_ENC_CAPS,
) -> Option<i32>

Query one NVENC capability of codec on an open session, returning the driver’s integer answer or None when the entry point is absent or the query fails — decide_caps reads None as “do not gate”, so a query failure never becomes a false refusal.